An ESD event commonly results from the discharge of a high voltage potential and leads to pulses of high current in a short duration (typically, 100 nanoseconds). Semiconductor IC is vulnerable to ESD events resulted by human contact with the leads of the IC or electrically charged machinery being discharged in other leads of the IC. Accordingly, an ESD protection circuit is essential to a semiconductor IC.
A parasitic silicon controlled rectifier (SCR) is one kind of on-chip semiconductor ESD protection device. Due to its high current sinking/sourcing capability, very low turn-on impedance, low power dissipation, and large physical volume for heat dissipating, parasitic lateral SCR devices have been recognized in the prior art as one of the most effective elements in semiconductor ESD protection circuits.
However, there is a major disadvantage with using the parasitic SCR device in ESD protection circuits, in that the parasitic SCR device has a high trigger voltage which could obstruct the parasitic SCR turning on timely to protect the semiconductor IC. Thus, in practice, some secondary protection elements, such as a field planted diode and a diffusion resistor, have to be incorporated with the lateral SCR device in order to provide an improved ESD protection. As a result, some additional processing steps and production cost for fabricating those elements may be required, and the layout size of the semiconductor IC can not be reduced.
Therefore, there is a need of providing an advanced semiconductor ESD protection apparatus in order to obviate the drawbacks and problems encountered from the prior art.